We are interested in the mechanisms by which RNA tumor viruses replicate and induce neoplastic transformation. The objectives of the proposed study include the elucidation of the biochemical nature of the oncornavirus 70S RNA genome and its transcription into DNA by the oncornavirus RNA-directed DNA polymerase. More specifically, we plan to address the nature of the oncornavirus 70S RNA genome, including the interactions responsible for the maintenance and formation of the 70S RNA complex, acquisition of host cell sequences (transduction) by the RNA tumor virus genome during infection, and the possible genetic recombination between two genetically unrelated avian oncornaviruses during mixed infection of avian cells. These studies will be performed by reannealing, hybridization and/or competition hybridization experiments and should reveal information regarding the nature and location of the sequences involved in the formation of 70S RNA, transduction and genetic recombination. Our continuing studies on RNA-directed DNA synthesis include a further analysis of the major species of primer RNA, characterization of additional 70S and 4S RNAs that can participate as primers and studies on the efficiency and extent of transcription of the genome RNA into DNA. The latter studies are directed at elucidating the exact requirements needed to transcribe genome RNA into unit length DNA chains in vitro to facilitate this transcription. We also plan to continue our studies on the effect, if any, of the oncornavirus RNase H activity on the transcription of genome RNA in vitro. Knowledge of the nature of both the oncornavirus genome and the RNA-directed DNA polymerase will be required before an understanding of the limitations and restrictions of reverse transcription, and therefore, the precise mechanism of RNA-directed DNA synthesis, and, ultimately, proviral DNA synthesis, can be attained.